A 5 GHz I/Q Phase-tunable CMOS LC Quadrature VCO (PT-QVCO) for Analog Phase Calibrated Receiver Architectures

This paper presents a 5-GHz phase-tunable I/Q signal generator in a 0.18 mum RF CMOS process based on the parallel cross-coupling of two -GM LC VCOs (QVCO). The proposed circuit achieves an ultra-wide I/Q phase tuning range without affecting the relative amplitude error or consuming additional power or chip area. Additionally, in restoring the phase balance, it is observed that the proposed method improves phase noise performance. Time domain measurements show that the two VCOs, prior to phase tuning, are quadrature locked with a 0.8deg phase imbalance and 1.4% relative amplitude error. In agreement with previously developed analysis, I/Q signals with phase error up to ~plusmn30 , beyond which the VCO cores are unlocked, can be driven to perfect quadrature phase. The PT-QVCO can be tuned from 3.87-4.45 GHz for the negative mode, and 4.4-5.4 GHz for the positive mode, a total of ~1.5 GHz. The fabricated circuit including pad structures occupies an area of 1.1 times 0.7 mm² and drains 18mW (excluding buffer circuits) from a 1.8 V supply voltage